Report Plugin: Deal with uploaded files when user Cancels edits

[samuel-kerrien]

Description Users can upload images in a given Analysis. Users can Cancel the editing of an analysis. Should images have been updated (and thus, stored in Delta), we need to take care of the clean up.

This ticket may be redundant if we decide to handle file upload differently. Specifically, we discussed the possibility of only submitting uploaded files to Delta upon saving a report. This way, we do not need to deprecate uploaded files if the user cancels. We need first to build a prototype and test it with users.

TODO [ ] Come up with a strategy [ ] Implement strategy